The statement gives the president wiggle room — something Obama has wanted to preserve throughout the two-year Syrian civil war. Combined with Obama’s call for to investigate and substantiate the assessment of the chemical use, Obama has now implied it would take a widespread use of the chemicals to prompt the U.S. to involve itself more deeply in the rebel effort to overthrow Assad, which is the stated objective of U.S. Syria policy. Foreign Policy managing editor Blake Hounshell suspected yesterday that it would take a much larger use of chemical weapons by Assad to spur a U.S. military response. But even “systematic” use of chemical weapons begs the question of how much sarin and other deadly gasses Assad can use before Obama feels compelled to stop him.

Syrians in the town of Kafranbel wonder what Obama will do in response to reports that Bashar Assad crossed the U.S. “red line” on chemical weapons use. Photo via @DavidKenner

It’s not clear when exactly the U.S. intelligence community came to believe Assad used his chemical arsenal. Britain, France and Israel have come to that conclusion. All a U.S. intelligence official would tell Danger Room — on background, is that “we recently came to the conclusion that Syria had likely used chemical weapons in the past.” The White House sent its Thursday letter in response to a Wednesday letter from eight senators inquiring about the allied intelligence assessment.

“The intelligence community has been working that target very hard, and has been doing our best,” said Lt. Gen. Michael Flynn, the director of the Defense Intelligence Agency, at a conference today. “The threshold of reliability, confidence and believability is definitely high, as it should be, because we do not want to– we have what we have in military force, but it’s not something we want to commit if we don’t have to.”

Unlike hawkish members of Congress, who are call for unspecified U.S. military action in Syria’s grinding civil war, the White House is reacting cautiously. Former officials like Steven Simon, who until December served as Mideast policy director on Obama’s National Security Council, told Danger Room that White House messaging has sought to convey to Assad that he dare not use his chemical stockpile without locking Obama into any set military action. “There’s no automaticity to any response,” he said.

Simon said Obama has options short of war. One is urging the International Criminal Court to indict Assad as a war criminal. Another is to increase aid to the Syrian opposition. “Apart from those two options there’s not a whole lot short of intervention,” Simon said, “but I don’t think they’re close to military intervention at this point.”

Among the administration’s concerns is that it’s far, far easier to involve the U.S. in Syria’s war than it is to extricate itself from it. There is nearly no appetite within the Pentagon for a third war in the Mideast and South Asia in 12 years. Military officials, like Gen. Martin Dempsey, the Chairman of the Joint Chiefs of Staff, have talked vaguely about planning options for direct U.S. military action. But no one within either the administration or the military has explained how to overthrow Assad; secure his chemical stocks; install a non-extremist successor government; secure the country; and leave. The chaos of Iraq and Afghanistan hint at another complication: U.S. involvement in the war does not guarantee the security of the chemical stocks; and runs the risk of getting U.S. soldiers and marines gassed.

“The idea that U.S. military action will prevent the spreading or damage from chemical weapons, it could be the opposite,” says Greg Thielmann, a former State Department intelligence analyst. You can’t just blow up sarin stockpiles, after all — not without risking some rather toxic results. “What other kinds of actions are being proposed here?”

There are good reasons not to go to war in Syria: mainly, the dubious U.S. national interests implicated. Obama is reluctant to spend blood and treasure there, and as much as hawkish rivals like Sen. John McCain (R-Ariz.) call Obama’s reluctance “shameful,” hawks have not provided a credible military plan of action.

But when Obama calls the use of the chemicals a red line, he boxes himself into some kind of response when the line is crossed. Moving the line — or, depending on your point of view, clarifying it — by talking about a “systemic” use of the weapons neither solves the dilemma nor sends Assad a clear message deterring the Syrian dictator from gassing his enemies. Much as Obama wants time and leeway, by talking about a red line at all, even to preserve the international consensus against chemical weapons use, Obama risks forcing his own hand for a war he does not want.

“I understand how Obama has boxed himself in with this bright red line, but I don’t understand those who argue for immediate action now, but the Syrian govt may have stepped over the red line, and how does this work?” Thielmann, now at the Arms Control Association, added. “I’m not sure Obama was as careful as he should have been when he warned Assad about it. … One should not get in the position we seem to be in, with a less-than-high-confidence assessment of CW use leaving us, according to John McCain and others, no alternative to intervene massively on the side of the rebels.”